Apparatus and method for PCB winding planar magnetic devices

Abstract

A method and apparatus to layout planar magnetic coils on a PCB consists of maximizing the layer to layer overlap, and consequently maximizing total inductance for the given layout area, by spiraling alternating layers inward and outward. A further benefit of the matching opposite spirals is the ability to make the layer to layer electrical contacts within the magnetic field area, thus reducing leakage inductance, and minimizing the wasted extra conductor line length needed to make the connections outside the magnetic field. The reduced conductor line length results in reduced conductor line resistance. The method is applicable to voltage transformers and isolation transformers as well as simple inductors and other magnetic devices. In the transformer case the odd numbered layers are typically connected together in series to provide a larger turn ratio, and the even numbered layers are typically single turns (i.e., no spiral) connected together in parallel to provide more current capability.

What is claimed is:  
     
       1. An apparatus for planar magnetic windings on a PCB having a plurality of conductive layers, comprising: 
       a plurality of electrical conductor lines formed into planar coils, wherein a plurality of the planar coils spiral inward and a plurality of the planar coils spiral outward,  
       each planar coil being disposed upon a different one of the plurality of conductive layers of the PCB in a vertical stack such that the spirals of the planar coils of the plurality of conductive layers are alternating inward and outward interleaved from one conductive layer to another,  
       said alternating and interleaved spirals of the planar coils enabling  
       (a) electrical connections between the planar coils to be inside a magnetic field area of the coils, and  
       (b) relatively better usage of conductive material inside the magnetic field area by the planar coils remaining within the magnetic field area to make connections and thereby (i) reducing an overall length of the planar coils which reduces electrical resistance of the coils, and (ii) minimizing leakage inductance.  
     
     
       2. The apparatus of  claim 1  wherein further both of the pluralities of coils spiral in a clockwise direction. 
     
     
       3. The apparatus of  claim 1  wherein the magnetic field of the coils is produced by electric current changes in the plurality of coils. 
     
     
       4. The apparatus of  claim 1  wherein the PCB has the number of the plurality of conductive layers increased by the addition of a plurality of daughter boards, each daughter board having at least one conductive layer, attached to and in electrical communication with one of the planar coils of the PCB. 
     
     
       5. The apparatus of  claim 4  wherein the plurality of daughter boards, each having at least one conductive layer, are attached to one of the planar coils of the PCB in pairs on opposite faces of the PCB. 
     
     
       6. The apparatus of  claim 1  wherein the plurality of coils include odd numbered coils and even numbered coils, the odd numbered ones of the plurality of coils are each electrically connected together to form primary windings of a transformer, and the even numbered ones are electrically connected together to form secondary windings of the transformer. 
     
     
       7. The apparatus of  claim 6  wherein every other ones of the odd numbered coils are spirals inward toward a central core area in one of either a clockwise or counter clockwise direction, the remaining ones of the odd numbered coils are spirals outward from the central core area in the same one of either a clockwise or counter clockwise direction as the inward spirals, and all of the even numbered coils are single turn coils.